This invention is generally directed to positively charged liquid developer compositions, and moe specifically positively charged liquid developers comprised of a lecithin charge director and a specific blue pigment. More specifically, in one embodiment the present invention is directed to liquid developer compositions comprised of polymer particles, nonpolar dispersant liquids, the charge director lecithin, and a specific blue pigment available from BASF Corporation. The aforementioned liquid developer compositions of the present invention can be selected for development of images in various processes inclusive of xerographic processes, elecgtrostatic printing, and facsimile systems; color proofing processes; and the processes as illustrated in British Patent Publication No. 2,169,416, published July 9, 1986, the disclosure of which is totally incorporated herein by reference. Preferably, the positively charged liquid developer compositions of the present invention ae useful in imaging systems having incorporated therein imaging members, particularly layered imaging members that have been negatively charged, reference for example U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
Numerous patents disclose liquid developer compositions inclusive of negatively charged liquid developers with charge directors such as lecithin. There is disclosed in U.S. Pat. No. 3,554,946 liquid developers for electrophotography comprised of a carrier liquid consisting of a hydrocarbon, negatively electrostatically charged toner particles dispersed in the carrier liquid, and a pigment therein such as carbon black, aniline black, prussian blue, phthalocyanine red, and cadmium yellow. In accordance with the teachings of this patent, a copolymer is coated on the surface of the pigment particles for the primary purpose of imparting a negative electrostatic charge to these particles. Other patents disclosing similar liquid developer compositions include Nos. 3,623,986; 3,625,897; 3,900,412; 3,976,583; 4,081,391 and 3,900,412. In the '412 patent, there is specifically disclosed a stable developer comprised of a polymer core with a steric barrier attached to the surface of the polymer selected. In column 15 of this patent, there are disclosed colored liquid developers by selecting pigments or dyes, and physically dispersing them by ball milling or high shear mixing. Attempts to obtain color liquid developer compositions by the ball milling process described have been unsuccessful, particularly with respect to obtaining developed images of acceptable optical density in that, for example, the desired size for the latex particles is from 0.2 to 0.3 micron in diameter; and with ball milling techniques it is very difficult to provide a dispersion of carbon black or other pigment particles much smaller in size than about 0.7 to about 0.8 micron. Consequently, the addition of carbon black pigment particles, for example, to latex particles with a diameter of 0.2 to 0.3 micron result after ball milling in relatively small latex particles residing on the surface of the pigment particles.
Additionally, there is described in U.S. Pat. No. 4,476,210, the diclosure of which is totally incorporated herein by reference, liquid developers containing an insulting liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
With further regard to the British Pat. Publication No. 2,169,416, the disclosure of which is totally incorporated herein by reference, there are illustrated liquid developer compositions comprised of toner particles associated with a pigment dispersed in a nonpolar liquid, and wherein the toner particles are formulated with a plurality of fibers or tendrils from a thermoplastic polymer, and possess a charge of polarity opposite to the polarity of the latent image.
Furthermore, there is illustrated in copending application U.S. Ser. No. 846,164, the disclosure of which is totally incorporated herein by reference, stable black liquid developers comprised of an insulating liquid medium having dispersed therein black marking particles comprised of a thermoplastic resin core which is substantially insoluble in the dispersion medium, and chemically or physically anchored to the resin core an amphipathic block or graft copolymer steric stabilizer which is soluble in the dispersion medium; and wherein dyes comprised of a specific mixture are imbibed in the thermoplastic resin core with the mixture of dyes being dispersible at the molecular level, and therefore soluble in the thermoplastic resin core and insoluble in the dispersion medium. Furthermore, in copending application U.S. Ser. No. 946,548, the disclosure of which is totally incorporated herein by reference, there is illustrated dyed sterically stabilized polymer particle for incorporation into negatively charged electrophoretic liquid developers.
Of particular interest with respect to the invention of the present application is U.S. Pat. No. 3,926,825, which discloses a positive liquid developer containing a phthalocyanine, see for example working Example 3; however, there does not appear to be any teaching in this patent with respect to the selection of the phthalocyanine in combination with a lecithin charge director. Furthermore, in U.S. Pat. No. 4,275,136 blue is selected as a pigment for a liquid developer, there being no reference in this patent with regard to the combination of such a pigment with lecithin. Examples of patents disclosing developers with phthalocyanine include Nos. 4,252,565 and 4,539,284. Furthermore, diclosed in U.S. Pat. Nos. 2,997,398; 3,082,171; 3,166,510; 4,056,494; 4,305,853; and 4,520,153 are the use of lecithin in dry electrophotographic inks and pigmented paints in coating compositions. Also of background interest are U.S. Pat. Nos. 4,707,429 relating to metallic soaps as adjuvants for electrostatic liquid developers; 4,702,985 directed to amino alcohols as adjuvants for liquid electrostatic developer; 4,702,984 relating to polybutylene succinimide as adjuvants for electostatic liquid developers; 4,681,831 directed to chargable resins for liquid electrostatic developers comprising partial esters of 3-hydroxy propanesulunic acid; 4,670,370 relating to processes for the preparation of colored liquid toners; 4,663,264 directed to liquid electrostatic developers containing aromatic hydrocarbons; and No. 4,631,244 relating to process for the preparation of liquid developers with polar additives for electrostatic imaging processes.
Other prior art of interest includes U.S. Pat. Nos. 4,454,215 and 4,058,774 directed to liquid developers, and more specifically suitable toner particles present in a specific liquid carrier so as to form readily disassociated flocs, reference column 4, lines 63 to 68, and continuing on to column 5, lines 1 to 14. Patents primarily of background interest are Nos. 4,306,009; 4,363,863; 4,374,918 and 4,521,505.
Although the above described liquid developers are suitable for their intended purposes, there remains a need for improved liquid developers, particularly those that can be positively charged. There also remains a need for liquid developers that can be selected for rendering visible images present on negatively charged layered photoconductive members. Furthermore, there is a need for liquid developers with excellent transfer efficiencies and suitable optical densities. Also, there remains a need for developer compositions useful in single pass two color electrophotographic imaging processes.
Furthermore, there remains a need for positively charged liquid developers which can be selected for discharge area development on positively charged imaging members such as selenium or selenium alloy photoreceptors.